Predicting the benefits of signal co-ordination.

This paper reviews the methodology and results of a study commissioned by Gwent County Council to assess the potential benefit of co- ordinating traffic signals and pelicans in the central area of Newport. In particular the study evaluated the benefits likely to be achieved from the introduction of SCOOT, and use was made of the Transport and Road Research Laboratory's computer program COORDBEN. The case for co-ordination is clear on routes with closely-spaced installations, dominant main road traffic movements, and high levels of tidality, such as exist on radial arterials, and the benefits achieved by fixed-time and SCOOT co-ordination under such circumstances are well established and widely documented. With the extra flexibility afforded by traffic-responsive co-ordination systems (SCOOT), co-ordination has more recently been introduced on main roads through central areas where conflicting and complex traffic patterns exist, and has often achieved significant benefits. The quantification of these benefits has however often resulted from "before and after" studies rather than from an evaluation of delay savings prior to implementing the new control system. Using the relationships within the COORDBEN program, potential benefits of SCOOT have been evaluated taking into account the specific traffic and junction characteristic within Newport. The central area of Newport is characterised by relatively high levels of traffic throughout the working day, with over-capacity at certain critical junctions during peak times. Traffic is variable in the short and long term, and complex conflicting patterns of movement exist. The potential for achieving co-ordination benefits has been assessed with reference to a review of traffic conditions, link characteristics and `natural' cycle times within the Newport network. This review also provides a basis for an assessment of whether or not the assumptions within COORDBEN are relevant and valid in the Newport context, and hence the program's ability to accurately predict benefits on this particular network.